The present invention relates to a bladder-actuated low-profile railroad retarder that is particularly suited for a railroad marshalling yard.
Bladder actuators are well known in the railroad industry. In 1882, the Smith Vacuum Brake included a sack or collapsing cylinder. The Firestone AIRSTROKE actuator developed in the 1930s includes upper and lower plates and a flexible bladder secured around the perimeter of each plate to form an airtight interior. The actuator is inflated and deflated to control its height. Down and up stops are used to set the minimum and maximum height or stroke length (SL) of the actuator. A bumper, a chain, a cable or metal stops can be located inside the actuator for this purpose. U.S. Reissue Pat. No. Re 33,207 discloses an on-board braking system using the Firestone actuator. U.S. Pat. No. 6,220,400 discloses a low profile, railway car retarder using the Firestone actuator. The actuator has an internal guide formed by two telescoping tubes, one of which has a stop ring at its end to form the upper and lower limit stops.
The railroad marshalling yard environment is dirty, rugged and non-stop. Retarders, switches, actuators, compressed air controls, related electric and electronic devices, and other components along tracks must withstand exposure to harsh weather, dirt, gravel, petroleum and other chemicals, and withstand being struck by moving objects carried by the cars. Moreover, actuators for retarders produce static vertical forces of about 20,000 pounds to generate the necessary braking power to control the speed of a fully loaded railroad car. Given this demanding environment, the railroad industry places great significance on minimizing maintenance and down time. Bladder actuators must withstand large cyclical loads and a harsh environment while maintaining low maintenance and down time requirements similar to conventional rigid cylinder actuators. The guide mechanism and limit stops of bladder actuators are often located inside the actuator for additional safety reasons.
A problem with railroad retarders is reducing maintenance to meet the demands of a busy marshalling yard setting. Evaluating fulcrum bearing wear is particularly problematic because the bearing is enclosed in the retarder. Conventional retarders must be disassembled to accurately and visually inspect of the bearing. Because closing a portion of the yard is impractical in a busy yard, maintenance personnel resort to using a pry bar to physically pry apart the upper and lower lever arms to determine if there is any wiggle occurring at the fulcrum bearing. Yet, this “wiggle” test is unreliable, particularly when done by a worker who is not familiar with the internal structure and mechanics of the retarder, and is not aware of the likely wear locations of the fulcrum bearing. If the pry bar is not inserted into the retarder and pushed or pulled in directions that will reveal the actual amount of wear, then the test may incorrectly indicate that little or no wear has occurred. Yet, a lack of proper inspection can result in an untimely failure of the fulcrum and retarder, which will then need to be replaced. Replacing a retarder is difficult to schedule because it requires a portion of the yard to be closed, which adversely impacts yard usage. Replacing a retarder during winter months when the ground is frozen is impractical.
Another concern with conventional retarders is the safety of yard maintenance personnel. The longer the workers are close to or in physical contact with the retarder, the more likely they are to be injured due to the daily risks associated with yard work. Inspecting bearing wear places workers at risk because the “wiggle” test requires a worker to stand on or near the retarder to manipulate the pry bar. The test is also inherently dangerous because of the awkward position and significant force a person must exert with the pry bar. Disassembling the retarder to inspect the bearing is even more involved, more time consuming, and more of a safety concern for the workers.
Another problem with conventional air bladder retarders is air consumption. The compressed air supply system for the yard has limited capacity. Conventional air bladder retarders use a significant amount of compressed air each time the retarder is activated. Installing numerous air bladder retarders throughout the yard can significantly increase yard air consumption. If the yard air system is already operating near capacity, installing air bladder retarders may require the addition of an air compressor or the replacement or overhauling of the of the air system. Yet, modifying or replacing the yard compressed air supply system is costly and time consuming, particularly regarding yard down time.
Another problem with air bladder retarders is life expectancy. Any crimping of the bladder during use can cause accelerated wear on the inside surface of the bladder. This wear weakens the bladder and can lead to premature rupturing. This problem is accentuated when the upper and lower plates of the bladder are pivotally connected to the lever arms by pivot pins. The pivot connections allow the plates to rotate, which can lead to undesired crimping. An additional guide mechanism is necessary to maintain the parallel alignment of the upper and lower plates of the bladder actuator. Bladder manufacturers set limits on the relative rotation of the plates when the bladder is in its fully extended or fully collapsed positions. Crimping can occur when the bladder is allowed to arc or accordion out due to relative rotation of the plates.
Another problem with conventional air bladder retarders is predictable use and service requirements. A problem with using an air bladder as an actuator for a railroad retarder is that it is difficult to identify or measure the wear on the bladder such as internal wear caused by crimping. Disassembling the actuator to inspect the bladder involves safety risks, maintenance costs and yard down time. Still, even a small leak in the bladder will waist yard air. Any unpredicted, premature rupture of the bladder will disable the retarder, lead to unplanned and costly replacement and down time, and increase safety risks to yard maintenance personnel.
Another problem with bladder actuators is the design of the guide mechanism. Some bladder actuators use an internal guide rod to form the upper and lower limit stops of the actuator as in U.S. Pat. No. 6,220,400. The guide rod experiences a tension load in excess of 20,000 pounds each time the actuator is opened. This cyclical load loosens the threaded engagement of the guide rod to the upper plate. Yet, maintaining the alignment of the guide rod is critical. Even a slight loosening of the guide rod can result in some lateral movement, which will exponentially increase the loads on and wear rate of the internal bushing or bearing. This loosening of the guide rod, or even the potential loosening of the guide rod, significantly increases the need for routine maintenance and possible down time. Other bladder actuators rely on the fulcrum pin to guide the movement of the actuator plates. Yet, the upper and lower plates for these bladder actuators also join the upper and lower lever arms via pivot pins. This construction can lead to crimping of the bladder, and result in leaks and unpredicted rupture of the bladder.
The present invention is directed to solving these and other problems.